The present invention relates to a charging device that is configured by serially connecting a DC-DC converter to a power supply device that outputs a direct current (DC) voltage. Further, the present invention relates to a charging device that is configured by serially connecting a plurality of power supply devices that output a DC voltage.
As disclosed in Japanese Patent Publication No. 2000-166114, a charging device that is configured by connecting a plurality of power supply devices in series has been known. Specifically, this charging device has a configuration in which a plurality of DC power supply devices having the same specifications are provided. Further, output terminals of a required number of the DC power supply devices are connected in series. As a result, a required high voltage can be obtained by adding each output DC voltage that is output from each of the serially connected DC power supply devices. In this charging device, each DC power supply device starts the operation at the same time and performs the charging for a battery pack that is composed with a plurality of secondary batteries. Further, in this charging device, a constant-current charging is performed for the battery pack while a charging current that flows in the battery pack and a charging voltage of the battery pack are detected. Then, when the detected charging voltage reaches a charge completion voltage that is defined in advance, the charging device stops the charging operation. Therefore, according to this charging device, a mass production effect of the DC power supply device can be pursued, and as a result, a low cost configuration of the device can be realized.
Further, according to the charging device explained above, the DC voltage is not generated from the DC power supply device over an entire generatable voltage range (for instance, 0-90 volts). The DC voltage is generated within a relatively narrow voltage range (for instance, 60-90 volts) because the use of a low voltage range that significantly lowers the power supply efficiency is to be avoided. As a result, the power supply efficiency of each DC power supply device can be increased.
The charging device described above, however, still has some problems to be solved. Specifically, the charging device explained above adopts the configuration in which a voltage range of the DC voltage that is generated by each DC power supply device is limited to the narrow range as explained above so as to increase the power supply efficiency. As a result, a battery for which a charging voltage is lower than the above limited narrow voltage range cannot be charged.